1. Field of the Invention
The present invention relates to an image display apparatus and a method which achieve enhancement of visual contrast of displayed images.
2. Description of the Related Art
In recent yeas, an image display apparatus provided with a light source and a light modulating device that modulates the intensity of light from the light source is widely used. A representative example is a liquid crystal display apparatus. However, in these image display apparatuses, the light modulating device does not have ideal modulation characteristics. Therefore, lowering of contrast caused by light leak from the light modulating device occurs especially when black image is displayed.
In order to improve the lowering of contrast, a plurality of methods in which luminance modulation of the light source in accordance with input image, conversion of gray-scales of the respective pixels of the input image, that is, gamma conversion, are combined are proposed.
For example, in SID Symposium Digest Vol. 38, pp. 1381, the luminance of a backlight and gamma conversion are determined on the basis of the highest gray-scale level of the input image.
In Japanese Patent No. 3215388, the luminance of the backlight and the gamma conversion are determined on the basis of the lowest gray-scale level, the highest gray-scale level, and the average gray-scale level of the input image.
Both of the technologies in the related art enable better amplification of the contrast by controlling the luminance of the light source and the gamma conversion of the input image in accordance with the input image in comparison with image display apparatuses on the basis of a constant light source luminance.
The both of the technologies in the related art control the light source luminance and the gamma conversion on the basis of representative values such as an average gray-scale level, a most frequent gray-scale level and a peak gray-scale level of the input image.
However, images which are significantly different in gray-scale distribution even though these representative values are the same exist in abundance, and there is a problem that sufficient contrast of the input image cannot be obtained since the same light source luminance and the gamma conversion are set up for all the images in the related art.
In view of such circumstances, it is an object of the invention to provide an image display apparatus and a method which achieve further enhancement of visual contrast of input images.